Cooktops have been developed in which radiant heating elements are mounted beneath a glass or ceramic panel. Such panels prevent contamination of the heating elements and provide a continuous surface that is easy to clean and enhances the appearance of the appliance in which the cooktop is mounted. However, while radiant heating elements typically radiate light as well as the heat for cooking, pans placed on the top surface of the panel obscure the visibility of the radiant light, particularly when a cooking pan is centered over the heating element for efficient heating. Moreover, even though electrical power to the heating element may have been shut off, the heating element may still remain hot even though the heating element does not radiate a visible indication of its temperature. Accordingly, previously known cooktops have employed a heat indicator lamp near the heating element or in the area of a control panel for the cooktop to indicate that a surface area of the cooktop remains at a high temperature. However, light displays that are small or only near to a portion of the heated area or in the case of placement in the control zone remote that may be from the heated area, such illumination does not provide a complete visual depiction of the heated area where inadvertent contact should be avoided.
Several problems must be overcome in order to improve the size of the area to be illuminated to more nearly correspond with the heated area. Increasing the surface area of the lighting subjects a large number of illuminating elements or substantial surface areas of large lighting elements to cyclic heating and cooling and the incident stresses and strains of such cycling. Moreover, the use of large lighting elements can illuminate substantially more than the surface area visible to the user, and may illuminate the entire interior of the appliance below the cooktop panel. Such illumination may detract from the appearance of the appliance as it illuminates far more details of the interior construction of the appliance than may be desirable. Moreover, proper positioning of the light at the heated area often requires special construction of the heater support or other mounting in order to incorporate the illumination at the heated area. Moreover, attempts to control illumination often resulted in the use of increasingly permeable coatings or thermochromic materials on the cooktop panel to control illumination through the heat radiating surface. Alternatively, multiple light sources may be employed at a particular area and selectively illuminated depending upon the temperature range of the heated area. Such illumination controls substantially increase the cost of the appliance and subject a substantially greater number of parts and surfaces to the stresses and strains of cyclic heating.